Colorspace Utility

Files
file	csp.h
	Colorspace value utility functions for libavutil.

Data Structures
struct	AVLumaCoefficients
	Struct containing luma coefficients to be used for RGB to YUV/YCoCg, or similar calculations. More...
struct	AVCIExy
	Struct containing chromaticity x and y values for the standard CIE 1931 chromaticity definition. More...
struct	AVPrimaryCoefficients
	Struct defining the red, green, and blue primary locations in terms of CIE 1931 chromaticity x and y. More...
struct	AVColorPrimariesDesc
	Struct that contains both white point location and primaries location, providing the complete description of a color gamut. More...

Typedefs
typedef AVCIExy	AVWhitepointCoefficients
	Struct defining white point location in terms of CIE 1931 chromaticity x and y.
typedef double(*	av_csp_trc_function) (double)
	Function pointer representing a double -> double transfer function that performs either an OETF transfer function, or alternatively an inverse EOTF function (in particular, for SMPTE ST 2084 / PQ).
typedef void(*	av_csp_eotf_function) (double Lw, double Lb, double c[3])
	Function pointer representing an ITU EOTF transfer for a given reference display configuration.

Functions
const AVLumaCoefficients *	av_csp_luma_coeffs_from_avcsp (enum AVColorSpace csp)
	Retrieves the Luma coefficients necessary to construct a conversion matrix from an enum constant describing the colorspace.
const AVColorPrimariesDesc *	av_csp_primaries_desc_from_id (enum AVColorPrimaries prm)
	Retrieves a complete gamut description from an enum constant describing the color primaries.
enum AVColorPrimaries	av_csp_primaries_id_from_desc (const AVColorPrimariesDesc *prm)
	Detects which enum AVColorPrimaries constant corresponds to the given complete gamut description.
double	av_csp_approximate_trc_gamma (enum AVColorTransferCharacteristic trc)
	Determine a suitable 'gamma' value to match the supplied AVColorTransferCharacteristic.
double	av_csp_approximate_eotf_gamma (enum AVColorTransferCharacteristic trc)
	Determine a suitable EOTF 'gamma' value to match the supplied AVColorTransferCharacteristic.
av_csp_trc_function	av_csp_trc_func_from_id (enum AVColorTransferCharacteristic trc)
	Determine the function needed to apply the given AVColorTransferCharacteristic to linear input.
av_csp_trc_function	av_csp_trc_func_inv_from_id (enum AVColorTransferCharacteristic trc)
	Returns the mathematical inverse of the corresponding TRC function.
av_csp_eotf_function	av_csp_itu_eotf (enum AVColorTransferCharacteristic trc)
	Returns the ITU EOTF corresponding to a given TRC.
av_csp_eotf_function	av_csp_itu_eotf_inv (enum AVColorTransferCharacteristic trc)
	Returns the mathematical inverse of the corresponding EOTF.

Detailed Description

Typedef Documentation

AVWhitepointCoefficients

typedef AVCIExy AVWhitepointCoefficients

Struct defining white point location in terms of CIE 1931 chromaticity x and y.

Definition at line 72 of file csp.h.

av_csp_trc_function

typedef double(* av_csp_trc_function) (double)

Function pointer representing a double -> double transfer function that performs either an OETF transfer function, or alternatively an inverse EOTF function (in particular, for SMPTE ST 2084 / PQ).

This function inputs linear light, and outputs gamma encoded light.

See ITU-T H.273 for more information.

Definition at line 91 of file csp.h.

av_csp_eotf_function

typedef void(* av_csp_eotf_function) (double Lw, double Lb, double c[3])

Function pointer representing an ITU EOTF transfer for a given reference display configuration.

Parameters

Lw	The white point luminance of the display, in nits (cd/m^2).
Lb	The black point luminance of the display, in nits (cd/m^2).

Definition at line 178 of file csp.h.

Function Documentation

av_csp_luma_coeffs_from_avcsp()

const AVLumaCoefficients * av_csp_luma_coeffs_from_avcsp

(

enum AVColorSpace

csp

)

Retrieves the Luma coefficients necessary to construct a conversion matrix from an enum constant describing the colorspace.

Parameters

csp	An enum constant indicating YUV or similar colorspace.

Returns

The Luma coefficients associated with that colorspace, or NULL if the constant is unknown to libavutil.

av_csp_primaries_desc_from_id()

const AVColorPrimariesDesc * av_csp_primaries_desc_from_id

(

enum AVColorPrimaries

prm

)

Retrieves a complete gamut description from an enum constant describing the color primaries.

Parameters

prm	An enum constant indicating primaries

Returns

A description of the colorspace gamut associated with that enum constant, or NULL if the constant is unknown to libavutil.

av_csp_primaries_id_from_desc()

enum AVColorPrimaries av_csp_primaries_id_from_desc

(

const AVColorPrimariesDesc *

prm

)

Detects which enum AVColorPrimaries constant corresponds to the given complete gamut description.

See also

enum AVColorPrimaries

Parameters

prm	A description of the colorspace gamut

Returns

The enum constant associated with this gamut, or AVCOL_PRI_UNSPECIFIED if no clear match can be identified.

av_csp_approximate_trc_gamma()

double av_csp_approximate_trc_gamma

(

enum AVColorTransferCharacteristic

trc

)

Determine a suitable 'gamma' value to match the supplied AVColorTransferCharacteristic.

See Apple Technical Note TN2257 (https://developer.apple.com/library/mac/technotes/tn2257/_index.html)

This function returns the gamma exponent for the OETF. For example, sRGB is approximated by gamma 2.2, not by gamma 0.45455.

Returns

Will return an approximation to the simple gamma function matching the supplied Transfer Characteristic, Will return 0.0 for any we cannot reasonably match against.

av_csp_approximate_eotf_gamma()

double av_csp_approximate_eotf_gamma

(

enum AVColorTransferCharacteristic

trc

)

Determine a suitable EOTF 'gamma' value to match the supplied AVColorTransferCharacteristic.

This function returns the gamma value (exponent) for a simple pure power function approximation of the supplied AVColorTransferCharacteristic, or 0. if no reasonable approximation exists.

EOTF(v) = (L_w - L_b) * v^gamma + L_b

Returns

Will return an approximation to the simple gamma function matching the supplied Transfer Characteristic EOTF, Will return 0.0 for any we cannot reasonably match against.

av_csp_trc_func_from_id()

av_csp_trc_function av_csp_trc_func_from_id

(

enum AVColorTransferCharacteristic

trc

)

Determine the function needed to apply the given AVColorTransferCharacteristic to linear input.

The function returned should expect a nominal domain and range of [0.0-1.0] values outside of this range maybe valid depending on the chosen characteristic function.

Returns

Will return pointer to the function matching the supplied Transfer Characteristic. If unspecified will return NULL:

av_csp_trc_func_inv_from_id()

av_csp_trc_function av_csp_trc_func_inv_from_id

(

enum AVColorTransferCharacteristic

trc

)

Returns the mathematical inverse of the corresponding TRC function.

av_csp_itu_eotf()

av_csp_eotf_function av_csp_itu_eotf

(

enum AVColorTransferCharacteristic

trc

)

Returns the ITU EOTF corresponding to a given TRC.

This converts from the signal level [0,1] to the raw output display luminance in nits (cd/m^2). This is done per channel in RGB space, except for AVCOL_TRC_SMPTE428, which assumes CIE XYZ in- and output.

Returns

A pointer to the function implementing the given TRC, or NULL if no such function is defined.

Note

In general, the resulting function is defined (wherever possible) for out-of-range values, even though these values do not have a physical meaning on the given display. Users should clamp inputs (or outputs) if this behavior is not desired.

This is also the case for functions like PQ, which are defined over an absolute signal range independent of the target display capabilities.

av_csp_itu_eotf_inv()

av_csp_eotf_function av_csp_itu_eotf_inv

(

enum AVColorTransferCharacteristic

trc

)

Returns the mathematical inverse of the corresponding EOTF.